Series regulator

Abstract

Disclosed are a series regulator and electronic equipment. The series regulator includes a first amplifier that drives a first transistor connected between a power supply and a load, a second amplifier that drives a second transistor connected in parallel to the first transistor, an amplifier control circuit that controls whether or not operation of the first amplifier is possible according to the load, and a first overcurrent protection circuit that limits a first output current flowing in the first transistor to a first overcurrent set value or smaller. The first overcurrent protection circuit carries out variable control of the first overcurrent set value according to a second output current flowing in the second transistor. The electronic equipment includes the series regulator and a load that receives power supply from the series regulator and operates.

What is claimed is: 
     
       1. A series regulator comprising:
 a first amplifier that drives a first transistor connected between a power supply and a load; 
 a second amplifier that drives a second transistor connected in parallel to the first transistor; 
 an amplifier control circuit that controls whether or not operation of the first amplifier is possible according to the load; and 
 a first overcurrent protection circuit that limits a first output current flowing in the first transistor to a first overcurrent set value or smaller, wherein 
 the first overcurrent protection circuit carries out variable control of the first overcurrent set value according to a second output current flowing in the second transistor. 
 
     
     
       2. The series regulator according to  claim 1 , wherein
 the first overcurrent protection circuit lowers the first overcurrent set value to a larger extent when the second output current is larger, and raises the first overcurrent set value to a larger extent when the second output current is smaller. 
 
     
     
       3. The series regulator according to  claim 1 , wherein
 current capability of the second transistor has power supply dependence or temperature dependence. 
 
     
     
       4. The series regulator according to  claim 1 , further comprising:
 a second overcurrent protection circuit that limits the second output current to a second overcurrent set value or smaller. 
 
     
     
       5. The series regulator according to  claim 4 , wherein
 the second overcurrent set value has power supply dependence or temperature dependence. 
 
     
     
       6. The series regulator according to  claim 1 , wherein
 the first overcurrent protection circuit includes
 a sense voltage generating unit that generates a sense voltage according to the first output current, and 
 a drive signal limiting unit that imposes limitation on a drive signal of the first transistor according to a difference value between the sense voltage and an overcurrent set voltage, and 
 
 an offset according to the second output current is given to at least one of the sense voltage and the overcurrent set voltage. 
 
     
     
       7. The series regulator according to  claim 6 , wherein
 the sense voltage generating unit carries out current/voltage conversion of a total current of a first sense current according to the first output current and a second sense current according to the second output current to generate the sense voltage. 
 
     
     
       8. The series regulator according to  claim 1 , wherein
 current capability of the second transistor is lower than current capability of the first transistor, and 
 current consumption of the second amplifier is lower than current consumption of the first amplifier. 
 
     
     
       9. The series regulator according to  claim 1 , wherein
 the first amplifier and the second amplifier respectively drive the first transistor and the second transistor in such a manner that an output voltage applied to the load corresponds with a target value. 
 
     
     
       10. Electronic equipment comprising:
 a series regulator including
 a first amplifier that drives a first transistor connected between a power supply and a load, 
 a second amplifier that drives a second transistor connected in parallel to the first transistor, 
 an amplifier control circuit that controls whether or not operation of the first amplifier is possible according to the load, and 
 a first overcurrent protection circuit that limits a first output current flowing in the first transistor to a first overcurrent set value or smaller, 
 the first overcurrent protection circuit carrying out variable control of the first overcurrent set value according to a second output current flowing in the second transistor; and 
 
 a load that receives power supply from the series regulator and operates.